Non-linear quantizer for video coding

• US 6,347,116 B1
• Filed: 07/24/1997
• Issued: 02/12/2002
• Est. Priority Date: 02/14/1997
• Status: Expired due to Term

• Current Assignee: AT&T Intellectual Property I LP (AT&T, Inc.)
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: Haskell, Barin Geoffry, Schmidt, Robert Louis, Puri, Atul
• Primary Examiner(s): Rao, Andy
• Application Number:
  US08/899,096
• Time in Patent Office: 1,664 Days
• Field of Search: 348/384, 348/390, 348/403, 348/404, 348/405, 348/607, 348/408, 382/236, 382/239, 382/240, 382/242, 375/240-1-2
• US Class Current: 375/240.03
• CPC Class Codes: H04N 19/124 Quantisation
• CPC Class Codes: H04N 19/126 Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
• CPC Class Codes: H04N 19/13 Adaptive entropy coding, e.g. adaptive variable length coding [AVLC] or context adaptive binary arithmetic coding [CABAC]
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/186 the unit being a colour or a chrominance component
• CPC Class Codes: H04N 19/60 using transform coding
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 19/91 Entropy coding, e.g. variable length coding [VLC] or arithmetic coding

Abstract

A quantizer and dequantizer for use in a video coding system that applies non linear, piece-wise linear scaling functions to video information signals based on a value of a variable quantization parameter. The quantizer and dequantizer apply different non linear, piece-wise linear scaling functions to a DC luminance signal, a DC chrominance signal and an AC chrominance signal. A code for reporting updates of the value of the quantization parameter is interpreted to require larger changes when the quantization parameter initially is large and smaller changes when the quantization parameter initially is small.

Claims

1. A quantizer for scaling a video information signal comprising:

a scaling factor generator that generates a scaler based on an at least three-segment piece-wise linear transformation of a received quantization parameter Q_p, and

a divider for dividing the video information signal by the scaler.

2. The quantizer of claim 1, wherein the scaling factor generator includes a memory in which the scalers are stored.

3. The quantizer of claim 1, wherein the scaling factor generator is a processor that computes the scalers.

4. The quantizer of claim 1, wherein:

the video information contains luminance information,

the scaling factor generator generates a luminance scaler,

the divider divides the luminance information by the luminance scaler and generates a luminance level signal therefrom.

5. The quantizer of claim 4, wherein the luminance scaler is generated from a piece-wise linear luminance scaling function based on the quantization parameter Q_p and

wherein the luminance scaling function equals 8 whenever the quantization parameter Q₂ falls within the values 1 through 4, inclusive;

wherein the luminance scaling function equals (2*Q_p) whenever the quantization parameter Q_p falls within the values 5 through 8, inclusive; and

wherein the luminance scaling function equals (Q_p+8) whenever the quantization parameter Q_p falls within the values 9 through 24, inclusive, and wherein the luminance scaling function equals (2*Q_p−

16) whenever the quantization parameter Q_p falls within the values 25 through 31, inclusive.

6. The quantizer of claim 1, wherein:

the video information contains DC chrominance information,

the scaling factor generator generates a chrominance scaler, and the divider divides the DC chrominance information by the chrominance scaler and generates a chrominance level signal therefrom.

7. The quantizer of claim 6, wherein the chrominance scaler is generated from a piece-wise linear chrominance scaling function based on the quantization parameter Q_p, and

wherein the chrominance scaling function equals 8 whenever the quantization parameter Q_p falls within the values 1 through 4 inclusive;

wherein the chrominance scaling function equals (Q_p+13)/2 whenever the quantization parameter Q_p, falls within the values 5 through 24, inclusive; and

wherein the chrominance scaling function equals (Q_p−

6) whenever the quantization parameter Q_p, falls within the values 25 through 31, inclusive.

8. The quantizer of claim 1, wherein:

the video information contains luminance and chrominance information,

the scaling factor generator generates a luminance scaler and a chrominance scaler by respective at least three-segment piece-wise linear transformations of the quantization parameter, and

the divider comprises;

a first divider that divides the luminance information by the luminance scaler and generates a luminance level signal therefrom, and

a second divider that divides the chrominance information by the chrominance scaler and generates a chrominance level signal therefrom.

9. The quantizer of claim 8, wherein

the luminance scaler is generated from an at least three-segment piece-wise linear transformation of the quantization parameter,

the chrominance scaler is generated from an at least three-segment piece-wise linear transformation of the quantization parameter, and

for all values of the quantization parameter, the chrominance scaler is less than or equal to the luminance scaler.

10. The quantizer of claim 1, wherein:

the video information contains AC chrominance information,

the scaling factor generator generates an AC chrominance scaler, and

the divider divides the AC chrominance information by the AC chrominance scaler and generates an AC chrominance level signal therefrom.

11. The quantizer of claim 10, wherein the AC chrominance scaler is generated from an a piece-wise linear AC chrominance scaling function based on the quantization parameter Q_p, and

wherein the AC chrominance scaling function equals 4 whenever the quantization parameter Q_p, falls within the values 1 through 4, inclusive;

wherein the AC chrominance scaling function equals (Q_p+13)/4 whenever the quantization parameter Q_p fills within the values 5 through 24, inclusive; and

wherein the AC chrominance scaling fiction equals (Q_p−

6)/2 whenever the quantization parameter Q_p falls within the values 25 through 31, inclusive.

27. The quantizer of claim 1, wherein the scaler is based solely upon the transformation.

12. A dequantizer for scaling a signal containing a quantized video information signal comprising:

a scaling factor generator that generates a scaler based on an at least three-segment piece-wise linear transformation of a received quantization parameter Q_p, and

a multiplier for multiplying the quantized video information signal by the scaler.

13. The dequantizer of claim 12, wherein the scaling factor generator includes a memory in which the scalers are stored.

14. The dequantizer of claim 12, wherein the scaling factor generator is a processor that computes the scalers.

15. The dequantizer of claim 12, wherein:

the quantized video information contains a luminance level signal,

the scaling factor generator generates a luminance scaler, and

the multiplier multiplies the luminance level signal by the luminance scaler and generates a luminance information signal therefrom.

16. The dequantizer of claim 15, wherein the luminance scaler is generated from a piece-wise linear luminance scaling function based on the quantization parameter Q_p, and

wherein the luminance scaling function equals 8 whenever the quantization parameter Q_p, falls within the values 1 through 4, inclusive,

wherein the luminance scaling function equals (2*Q_p) whenever the quantization parameter falls within the values 5 through 8, inclusive;

and

wherein the luminance scaling function equals (Q_p+8) whenever the quantization parameter Q_p falls within the values 9 through 24, inclusive; and

wherein the luminance scaling function equals (2*Q_p−

16) whenever the quantization parameter Q_p fills within the values 25 through 31, inclusive.

17. The dequantizer of claim 12, wherein:

the quantizer video information contains DC chrominance level signal,

the scaling factor generator generates a chrominance scaler, and

the multiplier multiplies the DC chrominance level signal by the chrominance scaler and generates a DC chrominance information signal therefrom.

18. The dequantizer of claim 17, wherein the chrominance scaler is generated from a piece-wise linear chrominance scaling function based on the quantization parameter Q_p, and

wherein the chrominance scaling function equals 8 whenever the quantization parameter Q_p falls within the values 1 through 4, inclusive;

wherein the chrominance scaling function equals (Q_p+13)/2 whenever the quantization parameter Q_p falls within the values 5 through 24, inclusive; and

wherein the chrominance scaling function equals (Q_p−

6) whenever the quantization parameter Q_p falls within the values 25 through 31, inclusive.

19. The dequantizer of claim 12, wherein:

the video information contains a luminance level signal and chrominance level signal;

the scaling factor generator generates a luminance scaler and a chrominance scaler by respective at least three-segment piece-wise linear transformation of the quantization parameter; and

the multiplier comprises;

a first multiplier that multiplies the luminance level signal with by the luminance scaler and generates a luminance information signal therefrom, and

a second multiplier that multiplies the chrominance level signal by the chrominance scaler and generates a chrominance information signal therefrom.

20. The dequantizer of claim 19, wherein

the luminance scaler is generated from an at least three-segment piece-wise linear transformation of the quantization parameter,

the chrome scaler is generated from an at least three-segment piece-wise linear transformation of the quantization parameter, and

for all values of the quantization parameter, the chrominance scaler is less than or equal to the luminance scaler.

21. The dequantizer of claim 12, wherein:

the quantized video information contains an AC chrominance level signal,

the scaling factor generator generates an AC chrominance scaler, and

the multiplier multiples the AC chrominance level signal by the AC chrominance scaler and generates an AC chrominance information signal therefrom.

22. The dequantizer of claim 21, wherein the AC chrominance scaler is generated from a piece-wise linear AC chrominance scaling function based on a quantization parameter Q_p, and

wherein the AC chrominance scaling function equals 4 whenever the quantization parameter Q_p falls within the values 1 through 4, inclusive;

wherein the AC chrominance scaling function equals (Q_p+13)/4 whenever the quantization parameter Q_p falls within the values 5 through 24, inclusive and

wherein the AC chrominance scaling function equals (Q_p−

6)/2 whenever the quantization parameter falls within the values 25 through 31, inclusive.

28. The dequantizer of claim 12, wherein the scaler is based solely upon the transformation.

23. A method of quantizing a video information signal, comprising the steps of:

generating a scaler based on an at least three-segment piece-wise linear transformation of a quantization parameter Q_p received with respect to the video information, dividing the video information signal by the scaler, and outputting the divided video information signal.

24. A method of dequantizing a quantized video information signal, said video information signal characterized by a plurality of macro blocks, each macro block quantized according to a respective quantization parameter, the method comprising the steps of:

receiving the quantized video information signal identifying the macro blocks,

identifying a quantization parameter update from the quantized video information signal,

generating a quantization parameter change based on the quantization parameter and the quantization parameter update,

generating a scaler for the macro block based on an at least three-segment piece-wise linear transformation of the quantization parameter and the quantization parameter change, and

multiplying quantized video information of the macro block by the scaler to obtain dequantized video information.

25. An encoder for encoding video signals, comprising:

a processing circuit that generates blocks of video data from the video information signal,

a transform circuit that generates video coefficients representative of the blocks of video data,

a quantizer circuit that receives a quantization parameter and quantizes the video coefficients according to an at least three-segment piece-wise linear transformation of the quantization parameter, and

a variable length coder that generates a variable length code based on the quantized video coefficients.

26. A decoder for decoding encoded video signals, comprising:

a variable length decoder that generates quantized video coefficients from variable length coded contained within the encoded video signals,

a dequantizer circuit that identifies a quantization parameter associated with the video information and dequantizes the video coefficients according to an at least three-segment piece-wise linear transformation of the quantization parameter,

an inverse transform circuit that transforms the dequantized video coefficients into blocks of video data, and

a processing circuit that generates a video signal from the blocks of video data.

29. A method of generating a dequantized DC luminance coefficient from a quantized DC luminance value, comprising:

retrieving a DC luminance scaler from an at least three-segment piece-wise linear luminance quantizing function bawd on a quantization parameter (Q_p); and

generating the DC luminance coefficient by multiplying the quantized DC luminance value by the DC luminance scaler.

30. The method of claim 29, wherein a relationship between the DC luminance scaler and the quantization parameter Q_p is given by Table 1.

31. The method of claim 29, wherein the DC luminance value is a member of an intra coded block of video data.

32. The method of claim 29, further comprising receiving the quantization parameter and the DC luminance value from a channel.

33. A method of generating a dequantized DC chrominance coefficient from a quantized DC chrominance value, comprising:

retrieving a DC chrominance scaler from an at least three-segment piece-wise linear luminance quantizing function based on a quantization parameter (Q_p); and

generating the DC chrominance coefficient by multiplying the quantized DC chrominance value by the DC chrominance scaler.

34. The method of claim 33, wherein a relationship between the DC chrominance scaler and the quantization parameter Q_p is given by Table 1.

35. The method of claim 33, wherein the DC chrominance value is a member of an intra coded block of video data.

36. The method of claim 33, further comprising receiving the quantization parameter and the DC chrominance value from a channel.